Mixing valves are well known and common in the plumbing field. These valves provide a flow of mixed water from separate hot and cold water supplies. Secondly, thermostatic control for handle mixer valves are well known. One reason for thermostatic control is to eliminate constant readjustment of the valve when the temperature of the hot water supply fluctuates. The temperature of the hot water supply may vary substantially. Furthermore, the pressure within the cold water line may also vary thus changing the proportions of hot and cold water flow and thereby fluctuating the temperature of the mixed water.
Known thermostatic valves have packaging problems and are often significantly bulkier than standard mixing valves that do not incorporate the thermostatic regulation. This bulkiness is due to the flow path that has always been used for thermostatic faucets, namely the supply inlets approach the centrally located thermostatic valve from a radially outer position.
When thermostatic valves are incorporated into mixer valves, the volume or flow control valves may be installed either downstream or upstream from the thermostatic valve element. When the flow is regulated downstream of the thermostatic element within the mixed water flow, installation of non-return valves are needed in order to prevent the possibility of communication between the hot water supply and the cold water supply. When volume control of the hot and cold water supplies is upstream of the thermostatic valve before the water is mixed, the return valves are not needed. For this economic reason, most thermostatic mixing valves have the volume control upstream of the thermostatic element.
However when the flow is regulated with respect to the hot and cold water supplies, the thermostatic device is unable to maintain the constant temperature due to the variations of the flow rates. It is well known that when hot and cold water supply pressures are approximately equal or with the hot supply pressure being only slightly lower than the cold water pressure, the difference in flow rate or variation between the hot and cold water supplies is increased when the total flow is reduced and the rise in temperature can sometimes become significant. On the other hand, if the hot water supply pressure is substantially lower than the cold water supply pressure, as in often the case due the increased corrosion of the hot water pipelines, the difference in the flow rate or variation of the flow rate between the hot and cold water supplies is decreased as the total flow rate is reduced.
Contoured apertures in a pair of disc plate valves have been known to contour the water flow profile between the hot and cold water supplies. However, these plate valves are set to move both rotatably and translationally with respect to each other to mechanically control both the total flow rate and the temperature mix of the hot and cold water.
What is needed is a compact thermostatic valve that is easily assembled and controls the temperature of the mixed water output. What is also needed is a thermostatic control built into a valve with flow control that provides proper thermostatic control at all flow rates.